(a) Field of the Invention
The present invention relates a power supply device and a driving method thereof. Particularly, a power supply device controlling a power supply according to a switching operation and a driving method thereof are provided.
(b) Description of the Related Art
An AC input voltage input to a power supply device is rectified, thereby becoming an AC line voltage. The AC line voltage is transmitted to a primary coil of a power supply device, and a primary current by the AC line voltage flows to the primary coil according to a switching operation of a power switch connected to the primary coil.
The primary current is increased during a period in which the power switch is in an on state, and an increasing slope of the primary current is changed according to an AC line voltage. If the drain current flowing to the power switch of the power switch reaches a predetermined reference value among the turn-on period, the power switch is turned off.
However, a predetermined delay period exists between a time that the drain current reaches the reference value and the power switch is actually turned off. The drain current is increased during the delay period. Thus, the drain current may be over a maximum current limitation value.
Particularly, the slope of the drain current is large when the AC line voltage is high such that the drain current is quickly increased during the delay period to be over the maximum current limitation value. This may damage the power switch.
Particularly, in a state in which an overload is connected to the power supply device, when the duty of the power switch is operated at maximum, the drain current being over the maximum current limitation value in the period in which the AC line voltage is high is frequently repeated. This may generate serious damage to the power switch.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.